Automation replaces the need for labor with a need for capital. That's labor in the form of whatever has been automated (by definition of automation), and capital in the form of machines, software, or whatever - it's capital if you can buy it and keep it. This increases the power of capital over labor. Because the top 0.1% are all capitalists, not laborers, this increases wealth concentration.

This isn't inherent to automation, but it is how we've structured our society to respond to automation.